In the last forty years, neuromodulation and neurostimulation implantable technologies have been used extensively for a variety of indications. As such, the components of these systems have developed a significant track record and their actions on the body are reasonably well understood. Many of these systems use implantable pulse generators (IPGs) and electrodes to deliver charge to the site of a biological tissue, e.g., a muscle or a nerve. By using low frequency and/or high frequency waveforms, the system induces action potentials in a targeted nerve (or nerves) that create the desired effect. It should be noted that the ability to create action potentials does not necessarily require direct contact with the nerve; however, certain applications may be most effective with direct nerve contact. One example is selective stimulation or recording from a portion of a nerve bundle. Another example is the blocking of conduction of action potentials using high frequency signals.
One example of a cuff electrode is a spiral cuff electrode that was patented in 1986 by Naples, Mortimer, et al (U.S. Pat. No. 4,602,624). It is a laminated assembly of two Silastic sheets (Dow Corning), with one layer stretched during the glue-up process (Silastic Adhesive). Once the assembly is freed from the press, it naturally curls towards the stretched side. The flat edge is typically long enough so that the cuff makes at least one and half revolutions of the nerve. This seals the cuff to provide an insulation barrier so that current does not leak around the cuff. The two laminates carry platinum electrodes, with spacing cut out on the stretched side so that current can be conducted inwards.
Some existing cuff electrodes do not reliability interface to small nerves. The stiffness of the platinum prevents the electrode from fully conforming to the small diameter of the nerve. The stiffness also does not allow the electrode to be fully adaptive, accommodating post-operative swelling of the nerve, which commonly occurs. Furthermore, the manufacturing process described in the Naples et al. patent to produce the electrode is hand-labor intensive with low repeatability of key process parameters.
Another example of a cuff electrode is a split cylinder cuff electrode that was patented in 2003 by Maschino et al. (U.S. Pat. No. 6,600,956). The split cuff configuration includes an electrode supporting matrix that supports a plurality of circumferential metallic electrodes. The matrix is injection molded to normally assume a curled, cuff shape. A split in the cuff allows the cuff to be opened to encircle a portion of a nerve. Once positioned, a fastener system is incorporated to close the cuff to prevent separation from the nerve. The fastener system reduces the ability of the cuff to expand about the nerve due to swelling, for example.
It is time that devices, systems, and methods employing a molded nerve cuff electrode provide improved manufacturability, consistent closing about the target nerve, and include the means to controllably manage increase or decrease in nerve size while maintaining the electrode to nerve contact pressure.